In order to isolate potential problem conditions on their telecommunication links, such as but not limited to those used for transporting digital data (such as T1 and High data rate Digital Subscriber Line (HDSL) signals), service providers conventionally had to dispatch a technician to one or more equipment locations, such as a central office or remote site. At a respective site, the technician proceeds to interface a piece of test equipment, such as a personal digital assistant (PDA) or test set, with the link under test (LUT) or with an external communication port (e.g. an RS-232 port) of a transceiver unit to which the link is coupled.
Due to the considerable cost, manpower and time consumption associated with this dispatch approach, many of the various pieces of communication equipment that make up such networks now include auxiliary capability, such as but not limited to loopback, status monitoring, and provisioning, which are selectively engagable through the use of prescribed stimuli codes that are injected into an in-band embedded operations channel (EOC) data stream from a supervisory test site.
A non-limiting example of such a code (that is not a rotation of any other similar code) employed by equipment manufactured by the assignee of the present application for initiating (loop query) diagnostic operations in remote equipment is the ‘DBDB’HEX sequence. In accordance with the use of this code, once a piece of equipment has been enabled for a particular diagnostic operation, such as a performance-monitoring loopback, it monitors the EOC for the presence of the code. Once the code (as transmitted in a repetitive sequence over a prescribed time interval (e.g., for several tens of seconds)) is detected, the interrogated piece of equipment will deliberately modify the received pattern being looped back to the initiating source, by the injection of errors at a prescribed rate or injection interval, to indicate whether or not measured performance (for example, in terms of signal quality and pulse attenuation) is satisfactory.
For example, if the defined parameters (e.g. signal quality (margin) and pulse attenuation) satisfy associated thresholds, the number of injected errors may be set at a first (relatively high) value, to indicate to the query source that the loop is operating satisfactorily, while the number of injected errors may be set at a second (relatively low) value, to indicate that loop performance is unsatisfactory. A shortcoming of this approach is the fact it does not indicate the ‘wellness’ of the loop; it only indicates whether the loop either passes or fails.
Because the thresholds against which performance is measured are customarily derived from some median set of criteria, a device returning a failure indication may actually be capable of providing a quite acceptable quality of performance for some period of time, before it becomes necessary to dispatch a technician for on-site testing and potential removal from service for upgrade or repair. Moreover, not all devices have the same level of maintenance/repair priority. It would be desirable, therefore, to have a more accurate picture of the performance capability of a remotely interrogated piece of equipment.